Exhaust nozzles of gas turbine engines generally comprise an axisymmetric exhaust centerbody centered therewithin in order to obtain an annular outlet for the flow of exhaust gas. A minimal amount of ventilation inside the centerbody is required to comply with engine certification requirements, since the cavity formed by the centerbody and the turbine section is a designated fire zone. Holes or slits can be provided on the centerbody in order to allow air to escape therefrom.
One example of known centerbody geometry is described in U.S. Pat. No. 3,970,252 issued Jul. 20, 1976 to Smale et al., which is incorporated herein by reference. The disadvantage of the film air outlets described by Smale et al., like many holes or slits known in the prior art, is that the hot exhaust gas can easily flow into the centerbody through the outlets, creating an undesired fire hazard and augmenting a risk of damage to nearby components of the engine. This phenomenon usually happens when the fluctuating pressure in the exhaust flow increases beyond the pressure of the gas contained within the centerbody. The negative pressure differential thus created acts as a vacuum to “suck” the exhaust flow inside the centerbody through the outlets, holes or slits.
A centerbody with flaps is shown in U.S. Pat. No. 3,910,375 issued Oct. 7, 1975 to Hache et al. When these flaps are opened, air is allowed to escape from the centerbody in order to obtain a more favorable noise signature. However, the open flaps cause an important blockage in the exhaust gas flow, causing it to accelerate and creating a severe disturbance which negatively affects engine performance.
Accordingly, there is a need for simple means to maximize an air flow out of the centerbody without significantly impeding engine performances.